1. Field of the Invention
This invention relates to a table driving apparatus, and more particularly to an apparatus for driving a working table in an X-Y direction to pick up or receive chip components which are to be mounted or assembled.
2. Description of the Prior Art
Such a working table, also called an X-Y table, is used in an automatic mounting apparatus for electric chip components such as transistors or capacitors and is usually driven in orthogonal directions (X and Y directions) in programmed sequence to pick up the chip components from a parts feeder and transport them to a printed circuit board for automatic mounting thereon (See, for example, U.S. Pat. No. 4,459,743). In another automatic mounting apparatus, the X-Y table carries a printed circuit board and moves to a predetermined position to receive thereon the chip components fed from the parts feeder. The working table can also be used with assembling robots for picking up the chip components and moving them to a predetermined position for assembling purposes.
The working or X-Y table is usually driven by means of X and Y drive motors through ball screws or belts. Such a working table driven by means of conventional motors requires many expensive parts of high precision and disadvantageously cause noise when they are driven. There is also a limit for the working table driven by means of the conventional motors when positioning accuracy is required or when movement at high speed is desired. For example, an assembling robot having a resolution of several microns and a moving speed of one meter per second can hardly be realized.
To overcome this drawback, a proposal has been made in which a direct-drive motor of a rotary type having a high resolution is used to drive the working table. When, however, the table is driven at high speed with high resolution using the direct-drive motor, there occurs another problem that an extraordinary oscillation or vibration takes place in a system including the direct-drive motor and a load coupled therewith because the dynamic characteristics of the direct-drive motor greatly depend upon a load coupled with it. To compensate for this oscillation, a filter is used in a driving circuit or a mechanical damper is incorporated in the system. These means are, however, less successful than expected because they need sophisticated adjustment.
It is therefore an object of the present invention to provide a table driving apparatus using a direct-drive motor which is capable of driving a working table with high resolution and high speed with simplified structure.
It is another object of the invention to provide a simple and stable table driving apparatus adapted for use with an automatic mounting apparatus or assembling robot.